Method and device for suppressing an explosion-like fire, in particular of hydrocarbons

ABSTRACT

There are described a method and a device for suppressing an explosion-like fire, in particular of hydrocarbons, by means of a fire extinguishing agent, which under pressure at a speed adapted to the speed of propagation of the fire is distributed in the space directly surrounding the source of the fire. To ensure an efficient fire fighting without adversely influencing the environment, it is proposed to spray water as fire extinguishing agent by atomizing the same to form a water mist in a minimum amount of 0.03 l/m 3  from a water reservoir (3) in the space directly surrounding the source of the fire.

This application is a 371 of PCT/AT95/00205, filed Oct. 19, 1995.

This invention relates to a method of suppressing an explosion-likefire, in particular of hydrocarbons, by means of a fire extinguishingagent which under pressure and with a speed adapted to the speed ofpropagation of the fire is distributed in the space directly surroundingthe source of the fire, and to a device for carrying out such method.

For suppressing explosion-like fires, in particular in vehicles withinternal combustion engines, it is known to use carbon halides, whichwith a speed adapted to the speed of propagation of explosion-likegasoline or oil fires are distributed in the space directly surroundingthe source of the fire to be expected. This distribution of the fireextinguishing agent in fractions of a second is achieved bypyrotechnically opening a correspondingly pressurized pressure vessel,from which the carbon halide being used is discharged in the space to beprotected under the acting pressure of the vessel. Due to ananticatalytic effect this carbon halide prevents an oxidation whichwould be sufficient for the propagation of the fire, without expellingthe oxygen from the space to be protected to an extent that endangers asurvival in this space. What is, however, disadvantageous in the use ofsuch carbon halides is their adverse effect on the environment. Inaddition, the cooling of the source of the fire achieved in connectionwith carbon halides is comparatively poor.

It is therefore the object underlying the invention to improve a methodof suppressing explosion-like fires, in particular of hydrocarbons, asdescribed above such that a very efficient suppression of the fire canbe ensured with an environmentally beneficial fire extinguishing agent.

This object is solved by the invention in that as fire extinguishingagent water possibly mixed with additives is distributed in a minimumamount of 0.03 l/m³ in the space directly surrounding the source of thefire by atomizing it to form a water mist.

The use of water or water mist for fighting a fire is of course known,but not for fighting hydrocarbon fires, where the use of water as fireextinguishing agent was avoided by all means. However, it wassurprisingly found out that explosion-like fires of hydrocarbons canalso be suppressed very efficiently by means of a water mist, when thewater mist from an amount of water of at least 0.03 l /m³ is sprayed inthe space directly surrounding the source of the fire. The use of waterin the form of a water mist leads to a very large surface of the waterdroplets as compared to the amount of water used, so that this amount ofwater evaporates very quickly by taking up a corresponding heat ofevaporation, which for fighting the fire involves a very advantageouscooling of the source of the fire, from which this heat of evaporationis withdrawn. This evaporation-related transition from the liquid to thegaseous state of the water droplets is in addition connected with a verylarge increase in volume (factor 1600), with the effect that the air andthus the oxygen in the direct vicinity of the source of the fire isexpelled by the steam produced, which prevents the oxidation requiredfor a propagation of the fire. This expulsion of oxygen must besufficient, which with the given changes in volume in the transitionfrom the liquid to the gaseous state requires a certain amount of waterper unit volume. The droplet size of the water mist does not play adecisive role, as it can be assumed that in a water mist the waterdroplets do not exceed a certain average size of about 400 μm, and thatwith this maximum droplet size the varying rate of evaporation as aresult of varying droplet sizes has no decisive influence on theexpulsion of oxygen.

What is, however, of major importance in the use of water mist for thesuppression of explosion-like fires is the evaporation of the waterdroplets controlled by the fire itself, which occurs to an increasedextent wherever there is an increased evolution of heat. As a result ofthe increased evaporation of the water mist with the increased evolutionof heat, the source of the fire is on the one hand cooled much more inthis local area, and on the other hand the oxygen is expelled from thisarea, which leads to the suppression of the fire. Outside such area ofevaporation the water mist atmosphere is maintained, so that a survivalin the space thus protected is ensured. In this connection it should bementioned that the radiant energy of the source of the fire isnoticeably reduced by the absorptive effect of the water droplets of thewater mist with increasing distance from the source of the fire.

For suppressing an explosion-like fire it is always required that thefire extinguishing agent can be distributed in the vicinity of thesource of the fire within a short enough period adapted to the speed ofpropagation of the fire. This is of course also true for the spraying ofwater mist. For this purpose, the spraying distance to the source of thefire must be restricted, and a sufficient acceleration of the sprayedwater must be ensured, so that the space in the direct vicinity of thesource of the fire can be filled with the water mist in thepredetermined minimum amount. When the water droplets of the water mistare sprayed with an average speed of at least 5 m/s, preferably at least10 m/s, at a distance of 1 m from the respective point of atomization,the usual basic conditions as regards the sources of fire to be foughtcan be satisfied very well. However, the predetermined minimum amount ofwater volume per unit of space must be ensured by a corresponding numberof nozzles.

It need probably not be emphasized particularly that not only purewater, but also water with additives, for instance with an antifreezeagent, can be used. However, the good evaporation of the water mustalways be ensured.

For carrying out the inventive method there can be provided at least onepressurized water reservoir, which by at least one control valve isconnected to nozzles directed against the space directly surrounding thesource of fire. To ensure that a water mist in an amount sufficient forthe method can be sprayed within a period adapted to the speed ofpropagation of an explosion-like fire in the space directly surroundingthe source of the fire to be expected, at least three, preferably fivenozzles per m³ of the space to be filled with water mist should beprovided in dependence on the throughput of the nozzles, where thecontrol valves must have a pyrotechnical opening means that can beactuated by a fire detector, so as to ensure an abrupt opening of thecontrol valves and avoid delays in the atomization of thecorrespondingly pressurized water as a result of the process of openingthe control valves. As fire detectors there may be used optoelectronic,thermoelectronic or acoustic sensors.

Another possibility of abruptly starting the atomization of the waterfrom a water reservoir connected to a pressurizing means consists informing the pressurizing means from a pressure chamber which is opentowards the water reservoir and is closed towards the same preferably bya pressure transmission element, in which pressure chamber a propellingcharge fitted with an ignition means is provided, so that the propellantgases produced upon igniting the propelling charge effect an expulsionof the water from the water reservoir through the attached nozzles,without having to actuate control valves.

To prevent water from flowing out of the water reservoir through thenozzles, the nozzles might at best be provided with closures openingunder a pressure, as this is achieved in the most simple case by a filmtearing under a certain pressure. The pressure transmission elementbetween the water reservoir and the pressure chamber does not onlyeffect an advantageous introduction of pressure into the waterreservoir, but also prevents a leakage of the propellant gases into thespace to be protected through the spray nozzles attached to the waterreservoir. To avoid any delay between the detection of the fire and thestart of the fire extinction, the ignition means for the propellingcharge must be actuated via a fire detector.

The inventive method of suppressing an explosion-like fire will now beexplained in detail with reference to the drawing, wherein:

FIG. 1 shows an inventive device for suppressing an explosion-like fireof hydrocarbons in a simplified block diagram, and

FIG. 2 shows an embodiment of an inventive fire suppression device,which has been modified with respect to FIG. 1, likewise in a blockdiagram.

In accordance with FIG. 1, a plurality of spray heads 1 are connected toa pressurized water reservoir 3 via control valves 2. When the controlvalves 2 are opened, the pressure acting on the water in the pressurizedwater reservoir 3 provides for the atomization of the water from thewater reservoir 3 in the spray heads 1, which for this purpose areprovided with nozzles not represented in detail. For abruptly openingthe control valves 2, the same are provided with pyrotechnical openingmeans 4, which are ignited via a control means 5 when a fire detector 6responds and the evaluation of the signals of the fire detector 6results in an actuation of the control valves 2 together or in a certainselection. After the abrupt opening of the control valves 2, the sprayheads 1 produce a water mist, which is sprayed into the space directlysurrounding the source of the fire, and within a short period, forinstance in about 100 ms, should reach a density which corresponds to anamount of water of at least 0.03 l/m³, preferably at least 0.05 l/m³. Tobe able to satisfy these conditions, all lines including those of thespray heads 1 must be filled with water, a sufficient number of sprayheads 1 must be provided, and a sufficient pressure must be applied tothe water to be expelled through the spray heads 1. In the case ofnozzle openings having a diameter of 1 mm and an appropriate design ofthe nozzles, an average speed of the mist droplets larger than 10 m/s isachieved at a pressure of 200 bar at a distance of 1 m from the sprayheads 1, so that the existing conditions can easily be satisfied. Theaverage diameter of the mist droplets is below 400 μm, for instanceabout 200 μm.

In accordance with FIG. 2 each spray head 1 is provided with a separatewater reservoir 3 verging into a pressure chamber 7, which has apropelling charge 8 with an ignition means 9. By means of a pressuretransmission element 10, for instance a piston, this propelling charge 8acts on the water of the water reservoir 3, which upon igniting theignition means 9 is abruptly sprayed from the spray heads 1. By thechoice of the propelling charge, the pressure acting on the water of thewater reservoir 3 and thus the speed of expulsion can be adjustedcorresponding to the respective requirements. The ignition signals forthe ignition means 9 are provided by a control means 5, which in turn isconnected with a fire detector 6 for evaluating the signals received.

The devices illustrated in FIGS. 1 and 2 in their basic configurationcan of course also be combined with each other, in that for instance apressure chamber comprising a propelling charge as proposed in FIG. 2 isassociated to the water reservoir 3 in accordance with FIG. 1.

Provided that as a result of the selection and arrangement of the sprayheads 1, an at least approximately uniform distribution of the watermist produced in the case of a fire is ensured in the space directlysurrounding the source of the fire, the illustrated devices provide fora very efficient suppression also of explosion-like fires ofhydrocarbons, without endangering a survival in the spaces to beprotected or adversely influencing the environment, because due to theevaporation of the water mist in the direct vicinity of the source ofthe fire an efficient expulsion of oxygen takes place and at the sametime the source of the fire is cooled by withdrawing the heat ofevaporation.

We claim:
 1. A method of suppressing the propagation of an explosivefire of liquid hydrocarbons, which comprises the steps of atomizingwater under pressure to form a water mist without a carrier gas, andspraying the water mist as a fire extinguishing agent in a minimumamount of 0.03 l/m³ at a speed adapted to the speed of propagation ofthe explosive fire to distribute the water mist fire extinguishing agentin a space directly surrounding a source of the explosive fire.
 2. Themethod of claim 1, wherein the minimum amount is 0.05 l/m³.
 3. Themethod of claim 1, wherein the water contains an additive.
 4. The methodof claim 1, wherein the water mist is sprayed at an average speed of atleast 5 m/s at a distance of 1 m from the point of atomization.
 5. Themethod of claim 4, wherein the water mist is sprayed at an average speedof at least 10 m/s at a distance of 1 m from the point of atomization.